Reproduction Carl Zeiss Jena Dokumar 8/38, adapted for mirrorless cameras. Review from Rodion Eshmakov

Review of the lens Carl Zeiss Jena Dokumar 8/38 specially for Radozhiva, prepared Rodion Eshmakov (subscribe to Instagram!).

The adapted CZJ Dokumar 38/8 has not lost its face.

The adapted CZJ Dokumar 38/8 has not lost its face. increase.

Dokumar lenses were manufactured in East Germany at the Carl Zeiss Jena factories around the late 40s and early 50s. These optics are designed for use with Dokumator reproduction systems. The lenses in the Dokumar range used a variety of optical designs and were apparently designed for use with different film formats:

  • Dokumar 35/5 - asymmetrical circuit, exactly unknown. Works at infinity only with APS-C mirrorless cameras;
  • Dokumar 35/2.8 - presumably "biometar" (5 lenses in 4 groups). Most likely, it also does not cover the full frame when focusing at infinity.
  • Dokumar 38/5.6 и 38/8 (presented in this article) - one and the same lens with a different constant aperture, optical design - "Russar" (6 lenses, 4 groups). Covers medium format 6 * 4,5 cm.
  • Dokumar 40/8 - "biometar" (5 lenses, 4 groups). Most likely, it covers the full frame.
  • Dokumar 47/5.6 - eight-lens "Russar" / "Distagon". (source). Covers medium format 6 * 6 cm.

All lenses are made in an aluminum body without aperture and focusing mechanism, with the exception of the Dokumar 35/5: it stands out for its heavy brass body and the presence of a six-blade diaphragm.

The most interesting are 35 / 2.8, 38 / 5.6 (8) and 47 / 5.6 lenses. The first is possibly a rare full-frame wide-angle lens for rangefinder cameras CZJ Biometar 35 / 2.8, converted for use at finite distances, while the 38 mm and 47 mm lenses use the original optical design of an ultra-wide-angle lens developed by Soviet optician Mikhail Mikhailovich Rusinov.

This article introduces the Carl Zeiss Jena Dokumar 38/8 modified for use with modern mirrorless cameras.

Specifications:

Optical design - 6 lenses, 4 groups (Russar);

Focal length - 38 mm;
Relative aperture - F / 8 (factory), F / 4 (after modification);
Frame format - up to 60 * 45 mm (covered), estimated unknown;
Rear focal segment - ~ 21 mm;
Features - does not have a focusing mechanism and an iris diaphragm (technical lens).

 

The history of Rusinov's ultra wide-angle lenses. aberration vignetting

Sources:

  1. http://www.marcocavina.com/articoli_fotografici/Hypergon_Topogon_Biogon_Hologon/00_pag.htm
  2. https://museum.itmo.ru/person/212/
  3. https://ru.wikipedia.org/wiki/Русинов,_Михаил_Михайлович
  4. https://dx.doi.org/10.1117/12.2246087
  5. http://www.photohistory.ru

Mikhail Rusinov was born into a family closely intertwined with music: his mother was a student of the pianist and composer A.G. Rubinstein at the St. Petersburg Conservatory, and his father worked there as a teacher of mathematics for scientific classes. Love for music was also passed on to Mikhail - later he loved to compose waltzes [1, 2, 3].

Rusinov began his education at a labor school (1917-1920), and then continued at the Professional School of Precision Mechanics and Optics (which later grew into ITMO). At the age of 18, Rusinov was already engaged in calculating the optics of submarine periscopes at LOMO, and at the age of 20-25 (1929-1934) he worked as a designer at VOOMP, the Main Directorate of Geodesy and Cartography. At the age of 23, within 10 years, he worked his way up from a senior engineer to the head of a laboratory and a senior researcher at the Central Research Institute of Geodesy, Aerial Survey and Cartography (TsNIIGAiK) [1, 2, 3].

During this period, Rusinov presented several ultra-wide-angle aerial photography lenses based on the Plasmata and Zeiss Topogon (Orion in the USSR) schemes - Liar-6 with a 104 ° field of view and Russar-1 with a 110 ° field, respectively [1].

Schematic diagram of the Russar-1 lens [1, 5]. This is not "the same" Russar yet.

Schematic diagram of the Russar-1 lens [1, 5]. This is not "the same" Russar yet.

The main problem of wide-angle optics of those times was vignetting, obeying the "cos4 law" (aka Lambert's law): the illumination of the center and the edge of the frame at an angle of view of 100 ° differed by more than 20 times! This forced the use of star-shaped diaphragms, which made it possible to reduce the difference in illumination at the cost of colossal light losses [1]. In subsequent years, a young scientist began to look for a way to bypass the limitations of Lambert's law.

Portrait of M.M. Rusinov (1909-2004), 1946.

Portrait of M.M. Rusinov (1909-2004), 1946.

Working at LITMO since 1930, Rusinov received in 1938 the degree of candidate of physical and mathematical sciences without defending a thesis [3]. In 1939, he developed an ultra-wide-angle 133 ° aerial photographic lens Russar-21, made according to a fundamentally new symmetric optical scheme with the use of large negative menisci [1]. The optical design was patented in Great Britain, France and the USA [5]. The era of wide-angle optics of a completely different quality has begun in the world.

Schematic diagram of the Russar-21 lens. The famous rangefinder ultra-wide-angle lens Russar MP-2 20 / 5.6, as well as Carl Zeiss Jena Dokumar 38/8, have the same.

Schematic diagram of the Russar-21 lens. The famous rangefinder ultra-wide-angle lens Russar MP-2 20 / 5.6, as well as Carl Zeiss Jena Dokumar 38/8, have the same.

In his lens, Rusinov was able to defeat Lambert's law: the illumination of the field of his lens fell according to the law cos ^ 3 θ, and not cos ^ 4 θ. Moreover, Rusinov's new lenses featured virtually zero geometric vignetting over a wide range of angles. Thus, the fall in illumination for an angle of 130 ° reached only 7 times (2,8 EV steps), while for the lenses that existed at that time at an angle of 100 °, as noted above, the illumination fell 20 times (> 4 steps EV) from the center to the edge of the image [1].

“That same” Russard exhibits much less vignetting than Topogon-like lenses of those years. Hypergon's even distribution of brightness throughout the frame is due to the use of a star-shaped aperture. [one]

“That same” Russard exhibits much less vignetting than Topogon-like lenses of those years. Hypergon's even distribution of brightness throughout the frame is due to the use of a star-shaped aperture. [one]


But not only this turned out to be good for the new lens: Russar-21 had practically zero distortion (0,1%!) And well corrected astigmatism [1]. These qualities made it ideal for aerial photography, reproductions, and accelerated the development of photogrammetry techniques.

The optical scheme developed by Rusinov turned out to be so successful that the famous German optician L. Bertele (a little about him: here и here ) was clearly inspired by her for the Carl Zeiss Biogon / Distagon lenses [1].

Bertele's 90 ° Biogon is clearly a loose interpretation of one of Rusinov's lenses. [one]

Bertele's 90 ° Biogon is clearly a loose interpretation of one of Rusinov's lenses. [one]

Soon after the development of Russar-21, Rusinov defended his doctoral dissertation in the field of technical sciences (1941) [3]. During the Great Patriotic War, he worked in Moscow at plant number 393 (future KMZ), was a professor at the Moscow Higher Technical School. Bauman. In 1944, however, he returned to Leningrad, where from 1946 he worked at ITMO [3].

M.M. Rusinov (center) [2].

M.M. Rusinov (center) [2].

In the same year, he presented his research in the development of ultra-wide-angle lenses to the general public, substantiating theoretically the phenomenon of aberrational vignetting [3] (hereinafter referred to in [4]).

The essence of theoretical research is not so complicated: it is known that the number of rays passing through the lens is determined by the size of its entrance pupil, the area of ​​which for oblique beams is usually smaller than for axial beams. This phenomenon is called geometric vignetting - we know it as, for example, the cause of the "swirling" bokeh of helios-like lenses and the dark corners of wide-angle lenses for SLR cameras. But it is important to remember that the entrance pupil is not inherently a physical object, but is an image of the aperture diaphragm (an area transparent to light that we see when we look at the lens from a distance from the front).

The aperture diaphragm of most lenses is located behind the lens relative to the entrance pupil of the system. Each lens introduces its own optical distortion, therefore the image of the aperture diaphragm, which is presented to us in the form of the entrance pupil, is distorted by the aberrations of the optical system. And here lies an important remark: with the help of the aberrations of the optical system, it is possible to control the size of the entrance pupil without changing the physical size of the aperture diaphragm.

In particular, the above publication [4] demonstrated the possibility of calculating an objective, the entrance pupil of which for off-axis beams is larger in area than for an axial beam. Thus, it is possible to introduce geometric vignetting into the system, which is used to correct field aberrations, without falling illumination across the field. This unique opportunity became part of the colossal contribution made by Mikhail Rusinov to the development of photographic optics.

M.M. Rusinov and the future founders of "7artisans" (a joke ... or not?). [2]

M.M. Rusinov and future founders "7artisans"(Joke ... or not?). [2]

Among his other achievements - the discovery of optical aberrations of the second order, the phenomenon of resolution of the center of the projection. After himself, he left more than a hundred scientific works, almost 300 inventions, 10 patents, as well as 7 doctors and 40 candidates of sciences prepared by him [2,3].

Design and adaptation features of the Dokumar 38/8

The Dokumar 38/8 is a technical lens and has no focusing mechanism or variable aperture. The rear focal length of the lens allows it to be used only on mirrorless cameras - taking this into account, choosing a focusing mechanism is not a problem. But the relative aperture F / 8 with such a focal length and dimensions looks very regrettable.

Lenses of the "Russar" type are, as a rule, artificially apertured (like RP-457). Dokumar is no exception. The role of a constant aperture is played by a fragment of the front lens unit housing. It can only be removed by the "barbaric method" by cutting it down with an engraver. In this case, there is a very significant risk of damage to the gluing of the front lens unit by the tool. Actually, the first time I was very unlucky, and the gluing of the front lens unit received damages incompatible with life. Fortunately, then I was able to find a donor lens and continue working.

Donor lens after lens unit replacement. Nearby is a cut off constant diaphragm.

Donor lens after lens unit replacement. Nearby is a cut off constant diaphragm.

The luminous diameter of the gluing of the front lens unit, however, is still slightly larger than the diameter of the hole in the housing at the place where the rear lens group is installed. However, I decided not to remove the lenses of the rear block and not to bore the case, since such an operation would not give a fundamental benefit.

Donor lens with front lens unit twisted. Nearby is a cut off constant diaphragm.

Donor lens with front lens unit twisted. Nearby is a cut off constant diaphragm.

Based on the initial and final diameters of the aperture diaphragm, the relative aperture of the lens after the upgrade is at least F / 4. This is not the best indicator for 35-40mm full-frame lenses, but quite normal for a medium format (Dokumar covers 6 * 4.5cm format) lens with such a simple optical design.

Donor lens with front lens unit twisted. Nearby is a cut off constant diaphragm.

Donor lens with front lens unit twisted. Nearby is a cut off constant diaphragm.

The Dokumar 38/8 has quite a bit of space for installing a diaphragm due to the small distance between the front and rear lens units. But the inner diameter of the case is quite sufficient. A fourteen-blade 18 mm diaphragm with a thickness of 5 mm was installed in the lens - for this it was necessary to slightly (~ 0.5 mm) increase the distance between the lens units. For symmetrical lenses, this does not lead to catastrophic consequences, slightly degrading the field performance. When moving, the blades of the diaphragm almost touch the surface of the lens of the front lens unit.

Dokumar 38/8 with installed iris diaphragm.

Dokumar 38/8 with installed iris diaphragm.

As a focusing mechanism, we chose the details of the helicoid of another Soviet technical lens, made according to the P-Flektogon scheme. For attachment to the camera, an M39 macro ring was used as a shank.

Dokumar 38/8 after adaptation.

Dokumar 38/8 after adaptation.

Although the minimum focusing distance with this focuser turned out to be about 25 cm, I used the thin M42-M42 macrogelcoid in combination with the M39-M42 and M42-FE (thin) adapters to get a larger macro zoom with an MDF of about 20 cm.

View of the adapted Dokumar 38/8 from the side of the M39 shank. Nearby is the M42-M42 macrogeloid, which is used instead of the M39-NEX adapter.

View of the adapted Dokumar 38/8 from the side of the M39 shank. Nearby is the M42-M42 macrogeloid, which is used instead of the M39-NEX adapter.

Due to the use of a symmetrical scheme and a considerable rear focal distance, the Dokumar 38/8 is inferior in size to lenses such as Jupiter-12 35/2.8 (Biogon Bertele mod. 1937/1950).

Dokumar is longer than Zorkiy BK 35 / 2.8 (prototype Jupiter-12)

Dokumar is longer than Zorky BK 35 / 2.8 (prototype Jupiter-12)

The nose of the Dokumar 38/8 is unusually large in comparison to other similar lenses.

The nose of the Dokumar 38/8 is unusually large in comparison to other similar lenses.

Dokumar 38/8 optics have a single layer of violet anti-reflective coating. The lens slightly shifts the maximum light transmission to the yellow region of the spectrum.

The pupil of the Dokumar 38/8 is much larger after the modification. A slight yellow tint of glass is noticeable.

The pupil of the Dokumar 38/8 is much larger after the modification. A slight yellow tint of glass is noticeable.

It can be noted that the full adaptation of the lens turned out to be not the easiest task: increasing the relative aperture requires rough intervention in the most vulnerable part of the lens, the installation of the iris diaphragm is also not easy. At the same time, the lens does not shine with parameters - it is a "dark" moderate wide-angle on a full frame, on a crop it is completely uninteresting about half a dollar.

However, Dokumar can be used without restrictions on mirrorless medium format cameras (EGF 30 mm on Fuji G cameras), moreover, it is a rare lens that uses the classic Russar six-lens scheme. Of the known lenses with such a scheme, only a very rare and expensive Russar MP-2 20 / 5.6, which was the only ultra-wide-angle lens for rangefinder cameras in the USSR. An expensive Zeiss Biogon 28 / 2.8 for Contax G cameras can be called a distant descendant of the Russar, which, however, is difficult to use on modern cameras due to the lack of manual focusing for this lens.

Optical properties

Dokumar shows a sharp image in the center from an open aperture. At the edges, sharpness is noticeably spoiled by field distortions up to f / 8. In this respect, it is not much better than the Zorkiy BK 35 / 2.8, but it is of higher quality than the serial Jupiter-12. At the same time, Dokumar has almost imperceptible distortion (after all, this is a symmetrical reproduction lens!) And near-zero vignetting - the merits of the used optical scheme of Rusinov.

Most likely, Dokumar is corrected to work at short focusing distances than at infinity - the lens performs well in macro photography. Moreover, the manifestation of chromatic aberrations, which, in ordinary lenses, often begin to make a large contribution to the image at high magnifications, is completely uncharacteristic of it.

Below are some trial examples of ~ 2: 1 macro photography on camera. Canon 600D using macro rings. Two shots are the result of stacking. The effect of diffraction on image quality is clearly visible.

Dokumar does not work very well with backlighting: single-layer coating does not prevent glare. In addition, a veil is added and some not quite well-blackened inner surfaces of the lens unit.

The bokeh of the lens is rather peculiar: the focus disc has a bright edging (“bubble”), closer to the edges of the frame, the discs turn into ellipses of approximately the same area. The resulting blurring of the background can be either smooth and soft, or bright and stand out. The Dokumar bokeh character is not similar to the usual old 35 / 2.8 lenses (for both SLR and mirrorless cameras), but very similar to the Contax G Biogon 28 / 2.8.

Below are examples of full-frame photos Sony A7s.

I cannot say that the lens has any outstanding characteristics: it is made according to a very simple optical scheme, has a low aperture, weak field sharpness. However, its picture is distinguished by the correct geometry, the absence of vignetting and chromatism, and pleasant bokeh characteristic of the more expensive optics of the Zeiss Biogon series.

Conclusions

Dokumar 38/8 is a German implementation of the classical MM scheme, rare among small-format optics. Rusinova, clearly demonstrating all of its key features. Today there are many wide-angle lenses of better quality and faster than Dokumar, but it is worth remembering that many of them (or rather, the original Rusinov lens) are their grandfathers.

You will find more reviews from readers of Radozhiva here.

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Comments: 41, on the topic: Reproduction Carl Zeiss Jena Dokumar 8/38, adapted for mirrorless cameras. Review from Rodion Eshmakov

  • B. R. P.

    Rodion, it seems to me: “The optical scheme developed by Rusinov turned out to be so successful that the famous German optician L. Bertele (a little about him: here and here) [HERE HERE] while developing Carl Zeiss Biogon / Distagon lenses [1].” a couple of words are missing.

    • Rodion Eshmakov

      Thanks, corrected

  • B. R. P.

    Photo caption M.M. Rusinov and the future founders of "7artisans" are from the heart.)

    • Rodion Eshmakov

      Delivers that together with Rusinov they are real 7.

      • Andrei

        “Craftsmen. Start."

  • Alexey

    An interesting article. I like to read historical excursions. Thank :)

  • Sergei

    In my opinion, the German Pentakta 30 mm / 2,8 for microfilming is much more interesting.

    • Novel

      I don't understand such comments. Review of the lens, and more a historical excursion, collectible value, notes about the history of optics, than an assessment of a promising lens present on the market. But there is someone, this someone has a VERY VALUABLE OPINION that some other lens is more interesting. SO WHAT?

  • Novel

    Thank you, as always interesting. Portraits at f / 8 are especially pleasing.

    • Rodion

      Portraits at F / 4.

      • Michael

        Did you try to shoot before the conversion to f8?

        • Rodion

          F / 8 before and after the rework does not differ dramatically.

  • Michael

    Arkady, typos:
    "Which in the future grew into ITMO"
    "Cos4 law"
    "Iris is just as tricky"
    "Chromatic aberration is not typical of conventional lenses."

    • Rodion Eshmakov

      Fixed thanks

  • Alexey

    Gorgeous alterations and reviews from the author.

  • Vladimir

    I am very pleased with this format of reviews, when a historical excursion and technical explanations are complemented by real experience. Thank!

  • axess

    Thank you for the historical insight, it was informative, I propose to open the type "Rodionozhivu" about Soviet rare lenses, their adaptation and history. By the way, the lens itself is not in the picture, well, it is not surprising in those years, but still interesting.

    • Rodion

      But why not something right away: better than most cheap 35 / 3.5 SLRs, for sure, especially in terms of the level of vignetting.

      • axess

        Probably not correctly expressed, I just did not get hooked, neither with the pattern, nor with the bokeh. And in terms of vignetting and sharpness across the field, it is possible that the Tessars will be stuck in the belt. thanks again for the review.

        • Rodion

          Oh, well, it's too dark to have any vivid picture features. Although in the summer, I think he would have shown himself better. Different seasons - different optics)

  • spitzer

    In contrast, it is quite passable and even not bad, not as hell as for 44x helios

    • Rodion

      In general, this lens is noticeably better in backlight than Jupiter-12 or Mir-1. He is also ahead in geometry and vignetting.

  • Vladimir

    Dear Rodion Eshmakov, thank you for sharing the result that this wonderful lens demonstrates. I myself use it on a film "Leica". However, an essay on the biography of Rusinov is absolutely inappropriate here. Unless, of course, we assume that “russar” is dokumar, great-grandson of angulon, angulon, great-grandson of russar, russar-great-grandson of planar, planar-great-grandson of dagor, dagor-great-grandson of aplanat ... .. In short, I don't even know whose biography is more appropriate here. But, I am outraged by the fact that you manipulatively, using the materials of MARCO cavina, did not mention a word the names of the REAL authors of this wonderful lens. WOLF DUNBERG and JOACHIM SCHILLING were not the sons of, the mother of a student of the pionist and composer A. G. Rkbinstern at the St. Petersburg Conservatory .... “(It was sarcasm for“ history lovers ”who did not understand) How could you pass off a drawing with an optical scheme of a Russar for a documar scheme? Where did you get the idea that the 38mm dokumar has six lenses? (give me a reference, please, if you want to argue with me ..) What makes you think that 38mm dokumar has a single layer of enlightenment? (please provide a reference, in the sense of a reference to a reliable source) Please do not mislead others, PUBLISHED at least once on an honest optical scheme of the 38mm documar, especially since you deliberately bypassed it and replaced it with a scheme ,, .... son of a student of the pionist and composer A. G. Rkbinstern at the St. Petersburg Conservatory ... "

    • Rodion

      If you want to refute what is stated in this article, then start with what you require of me: sources and evidence. I'm waiting.

    • B. R. P.

      You, too, TWICE, deliberately bypassed and replaced Anton Rubinstein with some kind of Rkbinstern. What to do now for fans of classical music, I do not know.

  • Vladimir

    By the way, he also does not cover the 6 / 4,5 cm format, this is also a lie from Rodion Eshmakov.

    • Novel

      Very loud accusations.

      https://www.flickr.com/photos/too_close_for_infinity/39806452993/ - here is an example of a photo on 6x6 film. If you crop to 6x4,5, there will be a strong vignette in the corners. It does not cover - it is debatable, but not an unconditional "no".

      The optical scheme is incomprehensible. Here is a list of all Dokumars: http://www.macrolenses.de/objektive.php?lang

      Your schema is taken from here - https://fotobabij.blogspot.com/2017/02/obiektyw-specjalny-carl-zeiss-jena.html?spref=pi

      It is completely identical to the scheme from here - http://www.marcocavina.com/articoli_fotografici/Zeiss_cute_DFR_DDR_lenses/00_pag_English.htm

      But here the Dokumar 47 / 5,6 is described. Where the Pole got his scheme from is completely unclear.

      One tiny fact speaks in favor of Rodion. He took it apart. I don't know if you or this Pole did the same.

      In your favor, of course, your indisputable authority speaks, in the end, education is not right now, mathematics is bad, Rodion could have been cheated out of inexperience.

      • Rodion

        There is a gallery of photos on Kiev-88 with the mirror removed and this lens: http://lens- club.ru/gallery/lens/c_7550.html
        Further, to determine the number of lenses in the glues is not the most trivial task, without completely disassembling the gluing, this is done by searching for reflections at the glass-glue-glass boundaries, which are much dimmer in comparison with reflections at the glass-air boundaries. Each of the lens units of this objective gives one dim reflection, i.e. gluing consists of 2 lenses. This is evidenced by the generally not the best lens correction at an average aperture. An eight-element lens would have significantly better quality.

        • Novel

          Rodion, where are you, and where is the owner of the Leike. Humble yourself and do not mislead the public with your falsified optical circuits, by God.

        • Novel

          By the way, judging by your gallery, it covers 6x6 without any problems.

          It is strange that the information on the documars - the cat cried. Apparently, no one really advertised the development for the Stasi.

  • StanislaVS

    The question of what hides or doesn’t hide is not really an idle one, since I planned to make such a lens on the Mamiya ZD, which has a 36x48 frame. There is enough working length for Mamiya 645 ash stump, since it was attached to Kyiv 88, but judging by this picture from the network, it does NOT fully cover frame 66.
    https://flic.kr/p/23DytD4
    And what is hidden? I cut out a 36x48 frame on a piece of paper in proportion to the 54x54 frame, attached it to the screen, it turns out to be covered, but at the limit, in the very corners, a small vignette can be seen. Those maximum somewhere 36x48 ... 37x49, film 645 format should not cover. Correct me if I'm wrong.

    • Rodion

      It was installed on Kyiv-88 by removing the mirror.

      • StanislaVS

        Thank you for answering, I have already figured out that it has no more than 55-65 mm from the rear edge of the case to the matrix, judging by the adapted copies, so there is no way on the Mamiya 645. Almost bought...

      • StanislaVS

        Do you happen to know how much it has from the rear edge of the case to the matrix and the diameter in the back?

        • Rodion

          Yes, I mean, in the review it is written in black and white - “Rear focal length - ~ 21 mm”, what kind of 55-65 mm are we talking about? The ZFD is considered from the lens, and from the edge of the case it will be a little less, it turns out.

  • StanislaVS

    So you yourself wrote that it covers the medium format ... :-) How is this possible with a focal length of 21 mm? :-) There is a direct relationship between the focal segment and the coverage circle. As for 55-65 mm, Avito sells an adapted copy of the mirror m39, they already have 45.5 mm, and the case does not stick out at the back, so I added another 10 mm, so it turned out 55-65 mm. If there really is 21 mm, as you write, then the question arises why it was necessary to push it into the Kyiv-88 case? Do you understand the absurdity of the statement about 21 mm? At such a distance, he should not cover the FF, not to mention the SF. :-)

  • StanislaVS

    There is a simple rule: the back focal length is approximately equal to the diagonal of the frame. If Dokumar 38, according to estimates on the verge, covers a 36x48 frame, the diagonal of which is 60 mm, hence I assumed that it has a segment of 55-65 mm. This rule has nuances, but on average it is.

    • Rodion

      You know, I remember you. You have already impressed with your excellent knowledge of optics when you simply brilliantly “analyzed” the Zenitar 50 / 0.95 optical design in the comments to this article: https://radojuva.com/2021/05/about-new-kmz-lenses/
      Now you again continue to “please” with your amazing calculations, which show your complete incompetence in the issues under discussion. The stubbornness with which you continue to talk nonsense is even enviable - but this is a consequence of only deep and hopeless mediocrity. Good luck!

      • StanislaVS

        Rodion, calling a person the simplest thing. I decided to buy this lens for a 36x48 frame, because I saw that someone was shooting with it at Kyiv 88. An internet search brought me to your review, which simultaneously states 1) that it covers the SF and 2) has a focal length of 21 mm . Why should I believe it? That's why I asked the question, and you began to call names ...

        You know, on such a popular resource lens. club one very popular blogger wrote that LOMO OKS 1-40-1 covers a 6x6 cm frame. I believed it, bought it, it turned out that it doesn’t even cover FF.

        Therefore, deal with your statements about the Dokumar 38 so as not to mislead people, since all requests for this lens lead to your article.

        Good luck!

        • Rodion

          Carrying nonsense is even easier. About OKS, one could understand that this is obviously nonsense, because it is well known that its optical design rarely gives a field of view angle of more than 55, read almost never. The Dokumar lens is made according to the Russkr orthoscope scheme, for which, with proper implementation, even 120 degrees is not the limit. And there is no connection with the back segment, this is generally a different scheme, for which the primitive calculations of the 19th century do not work.
          I do not see any point in discussing whether I have indicated the correct or incorrect focal length as well as other data. You can see everything in the photo, but the article says with which adapter the photos were taken, etc. Since you can’t read and then extract the necessary information, these are your problems and your stereotypes.

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